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Determinants of Breeding Distributions of Ducks

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Breeding Distributions of the Species

Blue-winged Teal.óBlue-winged teal had a distribution much like that of gadwall, with highest densities mostly in the prairie and parkland of Canada and the Dakotas (Fig. 8A), and was uncommon in the far-northern strata.


gif --Blue-Winged Teal Distribution

Figure 8. (A) Average species density by stratum, 1955-81; (B) correlation between species density and local pond counts, 1955-81; and (C) correlation between species density and total pond counts, 1955-81.

Most blue-winged teal winter in Central America or northern South America. Modest numbers are found in Mexico and in the Gulf Coast States (Bellrose 1980). Although a few may enter the major breeding area directly from the east, almost all return in the spring through the southern portal and are first exposed to wetlands in the Dakotas.

Densities of this species varied markedly with local pond counts (Table 3). Consistently high correlations were found in most strata where the species was common (Fig. 8B). Exceptions were in several strata along the northern and eastern edges of the core area that had large numbers of blue-winged teal, but teal numbers were not strongly associated with pond densities.

Blue-winged teal densities were positively related to total ponds in the eastern portion of the southern prairie provinces, northern Montana, all of North Dakota, and western South Dakota (Fig. 8C). Negative correlations were detected in the northern strata within its range and in the southern Alberta prairie, suggesting these strata as ultimate locations of drought-displaced birds. Blue-winged teal numbers were greater in strata in Alaska when the total number of ponds was low (Hansen 1960). Stoudt (1971) suggested drought displacement also to the south.

Breeding blue-winged teal are not philopatric (Table 4). In fact, they are considered strong pioneers; Bellrose (1980) reported several instances in which teal nested well outside their normal breeding range in response to newly flooded habitat.

Although not conclusive, the fact that correlations with pond counts were more related to average density of blue-winged teal than to latitude suggests that the birds do not simply fill their breeding habitat as they encounter it, but occupy the primary area first. If conditions there are not favorable, they move northward, or possibly back south.


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